1. Field of the Invention
The present invention relates to apparatus for modifying the gas atmosphere of individual trays containing e.g., foodstuffs, and for sealing the individual trays with the modified gas atmosphere.
2. Description of the Prior Art
The modern trend toward increased convenience in preparing meals has caused a significant and fundamental change in the way most foodstuffs are packaged and sold at retail stores. Rather than sell in bulk quantities, supermarkets and convenience stores typically market such foodstuffs as meats, poultry, dairy products, etc. in relatively small portions suitable for only a few servings. Typically, such foodstuffs are processed at a processing plant from bulk quantities into single or multiple serving sizes and packaged in individual trays. The trays generally have a flanged peripheral edge surrounding a recessed portion, and a clear film cover for display purposes.
A significant problem occasioned by the marketing of smaller sized portions of perishable foodstuffs is the possibility of increased spoilage rate and reduced shelf life. The smaller portions typically have a larger ratio of surface area to volume which accelerates the chemical and bacterial attack on the product. This problem has put a premium on the control of the atmosphere surrounding the packaged food stuffs. For example, there can often result the need to reduce or enrich the oxygen content of the atmosphere surrounding the foodstuffs to retard spoilage induced by chemical action and bacteria, in order to extend the shelf life and appearance of the foodstuffs.
Conventional tray wrapping/packaging machines, including those which attempt to replace or enrich the oxygen atmosphere by the use of a gas flush tunnel, vacuum chamber, or other component charged with an atmosphere-modifying gas, have not been entirely satisfactory or have proved more costly than desired due to the need, for example, of associated vacuum pump apparatus. Also, the intermittent motion and resulting slow cycle speeds which characterize conventional tray wrapping and packaging machines make them economically less attractive to operate. These shortcomings are believed to be the result of the additional complexity due to the tunnel components and vacuum chambers and the inability to completely "flush" the tray even using "vacuuming" techniques.